This invention relates to a testing equipment, and more particularly to an apparatus for measuring the internal friction of a metal specimen.
The technique of measuring the internal friction of a metal specimen is important in the study of metal. In particular, the internal friction measurement is the only exsisting method which can be used to determine the solute content of carbon and/or nitrogen in steel. There are two major conventional methods for measuring the internal-friction behavior. The first one is the torsion pendulum method in which one end of a metal specimen is hung so that it can be driven to cause torsional vibration. The amplitude of the vibration, after reaching a certain value, is then freely reduced. The amplitude attenuation of the vibration vs. temperature and some internal friction peaks can be obtained, with which many characteristics, such as point defects, dislocations, and grain boundaries of the metal, the distribution and diffusion parameters of some elements in an alloy, and so on may be investigated. The other method is the transverse vibration method in which a metal specimen is driven to cause a transverse vibration of the specimen. The amplitude of its transverse vibration, after reaching a certain value, is also freely reduced.
Referring to FIG. 1, a metal specimen 10 is placed on two spaced-apart supporting points 11 and 12 in a transverse vibration internal friction measurement. A drive means 13 which is usually a magnetic coil 13 being disposed near one end of the specimen 10. A detecting coil 14 is disposed near the other end of the specimen 10. The driving coil 13 and the detecting coil 14 may be replaced with electrostatic exciting and detecting devices.
The internal friction is represented by .theta..sup.-1 and can be obtained from the following equation; ##EQU1## where A.sub.o and A.sub.n are the starting and final amplitudes of free vibration decay in the calculation, respectively. In FIG. 2, A'.sub.o, although does not exist in the equation, is the very begining amplitude of free vibration decay.
FIG. 3 is a block diagram of a transverse vibration friction measuring system which includes a measuring apparatus 100. A vacuum is formed in the measuring apparatus 100 by a vacuum system 101. This vacuum is necessary for the proper measurement of a metal specimen 10. An assembly 102 of a driving member and a detecting member, a temperature sensing element 106 and a heating source 103 are mounted within the measuring apparatus 100. Normally, the temperature sensing element 106 is a thermocouple. The operation of the heating source 103 is controlled by a programmable temperature automatic control system 104 so as to provide an appropriate heating rate and final temperature to the measuring system. The temperature control system 104 is connected to a temperature detector 105 which can detect the ambient temperature of the specimen 10 by the temperature sensing element 106. The measuring system also includes a driving and detecting system 107 supervised by a frequency counter 108 which can provide cycle force of resonant frequency of the specimen. A counter 109 is used to count the number of the transverse vibration decay from amplitude A.sub.o to A.sub.n of the specimen 10. A display device 110 which is an oscilloscope is used to display the wave form of the transverse vibration of the specimen 10. The measuring system is equipped with a digital analysis computer system 111 which includes a disk drive 112, a keyboard 113, a printer 114 and a monitor 115. The computer system 111 is connected to the frequency counter 108, the counter 109 and the temperature detector 105 by a data bus 116 so as to analyze and calculate the vibration information of the specimen 10. The computer system 111 also control the starting of the driving and detecting unit 107 and can determine the operation time and temperature of the driving and detecting process so as to obtain the internal friction vs. temperature and the elastic modulus-temperature curves which help to understand the type of the internal friction peaks of the specimen 10.
Conventional internal friction measuring systems have disadvantage in that the specimen 10 is difficult to conveniently and accurately mount in the measuring apparatus 100. In addition, the assembly 102 of the driving member and the detecting member may burn down at a high temperature.